Conventional methods for treating elastic polyurethane yarns include 1) treating by a treatment agent with a higher fatty acid metal salt dispersed in polydimethylsiloxane or mineral oil (JP-B-SHO-37-4586, SHO-40-5557 and HEI-6-15745), 2) treating by a treatment agent with an amino modified silicone added to polydimethylsiloxane or mineral oil (JP-B-SHO-63-8233), 3) treating by a treatment agent with a polyether modified silicone added to polydimethylsiloxane or mineral oil (JP-B-SHO-61-459, and JP-A-HEI-2-127569 and 6-41873), 4) treating by a treatment agent with a silicone resin added to polydimethylsiloxane or mineral oil (JP-B-SHO-42-8438 and 63-12197 and JP-A-HEI-8-74179), 5) treating by a treatment agent with a n amino modified silicone an d a silicone resin added to polydimethylsiloxane or mineral oil (JP-A-HEI-3-294524, 3-51374 and 5-195442), etc.
In the method of treating an elastic polyurethane yarn by a treatment agent with a higher fatty acid metal salt dispersed in polydimethylsiloxane or mineral oil, the initial dispersed state of the higher fatty acid metal salt cannot be retained, which causes cohesion, settlement, etc. with the lapse of time. Since a treatment agent has remarkably low dispersion stability like this, the higher fatty acid metal salt coheres even if the treatment agent is sufficiently stirred when used. So, the elastic polyurethane yarn cannot have satisfactory reelability since the overlying segments of the yarn adhere to each other. Furthermore, since the cohering higher fatty acid metal salt drips and accumulates on guides during processing, it causes yarn breaking disadvantageously. Moreover, if a treatment agent having a large amount of a higher fatty acid metal salt dispersed is used, any matter dissolved from the fibers during processing raises the viscosity of the treatment agent after the lapse of time, and disadvantageously, stable operation cannot be achieved. If a treatment agent with a modified silicone such as an amino modified silicone, polyether modified silicone or silicone resin added to polydimethylsiloxane or mineral oil is used, the effect of preventing the adhesion between yarn segments in an elastic polyurethane resin package is weaker compared to the case of using a treatment with a higher fatty acid metal salt added, and satisfactory reelability cannot be obtained. Especially when a treatment agent containing an amino modified silicone or polyether modified silicone is used for treatment, the inter-fiber friction coefficient becomes very low, and the winding in the package is deformed and no good winding form can be obtained. Furthermore, low molecular components are dissolved out of the fibers, to drip and accumulate as scum on guides with the lapse of time, disadvantageously not allowing stable operation.